Abstract
Microglia are the resident immune cells of the brain, which are important therapeutic targets for regulating the inflammatory responses particularly neurodegeneration in the aging human brain. The activation, chemotaxis and migration of microglia are regulated through G-protein coupled receptors by chemokines such as stromal cell-derived factor (SDF)-1α and bioactive lysophospholipids such as lysophosphatidic acid (LPA). Potassium channels play important roles in microglial function and cell fate decisions; however, the regulation of microglial potassium channels has not been fully elucidated. Here we show reciprocal action of SDF-1α and LPA, on potassium currents through Kir2.1 channels in primary murine microglia. The potassium channel modulation is mediated by the same small GTPases, Rac and Rho that regulate the actin cytoskeleton. SDF-1α rapidly increased the Kir2.1 current amplitude and cell spreading. These effects were mimicked by dialysing the cells with constitutively active Rac1 protein, and they were blocked by inhibiting the phosphatidylinositol 3-kinase (PI3K) with wortmannin. In contrast, LPA and constitutively active RhoA decreased the Kir2.1 currents and stimulated cell contraction. Thus, SDF-1α and LPA regulate both the actin cytoskeleton and the Kir2.1 potassium channels through the same Rho GTPase signaling pathways. The inhibition of Kir2.1 with chloroethylclonidine produced cell contraction independently of chemokine action. This suggests that potassium channels are essential for the morphological phenotype and functioning of microglia. In conclusion, the small GTPases, Rac and Rho, modulate Kir2.1 channels and block of Kir2.1 channels causes changes in microglia morphology.